Conventionally, a gear device having a cylindrical portion that extends in an axial direction of the gear device is known. This gear device allows various types of cables or the like to be routed through the cylindrical portion.
Japanese Unexamined Patent Publication No. H9-57678 describes a slewing structure. The structure includes a crank pin, a pinion that has a plurality of outer teeth and that is swung and rotated as the crank pin is rotated, a case that has a plurality of pin teeth engaged with the individual outer teeth of the pinion, and a flange that rotatably supports the crank pin. In the slewing structure, while the case is secured to a stationary portion of a robot, the pinion is swung and rotated. As a result, the flange is rotated. The slewing structure also includes a cylindrical portion that extends through the pinion, the case, and the flange disposed in an axial direction of the slewing structure. The cylindrical portion is secured to the flange.
Japanese Unexamined Patent Publication No. 2001-323972 describes an eccentric swing type speed reducer that includes a crankshaft, an outer tooth gear that is swung and rotated as the crankshaft is rotated, an inner tooth portion engaged with the outer tooth gear, and a rotation portion that rotatably supports the crankshaft. In the eccentric swing type speed reducer, while the inner tooth portion is secured to a first joint portion, the outer tooth gear is swung and rotated. Thus, the rotation portion is rotated. The eccentric swing type speed reducer also includes a protection tube that extends through the outer tooth gear, the inner tooth portion, and the rotation portion in an axial direction of the eccentric swing type speed reducer. The protection tube is secured to the inner tooth portion through the first joint portion.
In the slewing structure described in Patent Literature 1, the cylindrical portion is secured to the flange that is disposed on a rotational side of the slewing structure. In other words, while the flange is rotated, the cylindrical portion is also rotated. Thus, for example, when a cable routed in the cylindrical portion is secured to the case disposed on the stationary side of the slewing structure so that the cable is not displaced relative to the case, the cable and an inner peripheral surface of the cylindrical portion are rubbed against each other.
On the other hand, in the eccentric swing type speed reducer described in Patent Literature 2, the protection tube is secured to the inner tooth portion disposed on a stationary side of the eccentric swing type speed reducer. In other words, while the rotation portion is rotated, the protection tube is kept in a stationary state. Thus, for example, when the cable routed in the protection tube is displaced relative to the inner tooth portion disposed on the stationary side of the eccentric swing type speed reducer, the cable and an inner peripheral surface of the protection tube are rubbed against each other.
Thus, depending on how a cable is used in the stewing structure described in Patent Literature 1 and the eccentric swing type speed reducer described in Patent Literature 2, the cable is rubbed against the inner peripheral surface of the cylindrical portion or the inner peripheral surface of the protection tube. As a result, the cable may be damaged.